1. Field of the Invention
This invention relates to improvements in an airbag restraint system for protecting a vehicle passenger in the event of a serious vehicle collision, and more particularly to an airbag which is configurated to be supplied with gas from a gas generator and formed by sewing a sheet material into a bag-shape, forming a sewed section, the sewed section including a low strength part which is adapted to be openable under an internal pressure of the airbag to form a gas leak opening through which gas in the airbag leaks out.
2. Description of the Prior Art
Hitherto a variety of airbag restraint systems for an automotive vehicles or the like have been proposed and put into practical use in order to protect passengers in the event of a serious vehicle collision. It is well known that an airbag of the airbag restraint system is arranged to momentarily inflate under supply of gas from a gas generator in the event of a serious vehicle collision thereby to safely restrain the vehicle passenger, in which a part of gas within the airbag is discharged thereby lightening a reaction against the vehicle passenger. Such an airbag restraint system is disclosed, for example, in Japanese Utility Model Publication Nos. 56-12139 and 54-3485, in which the sewed section of the airbag includes a low strength sewed part which is adapted to be openable during inflation of the airbag thereby to form a gas leak opening through which a part of gas within the airbag leaks.
However, difficulties have been encountered in such a conventional airbag restraint system, in which there is a possibility that the sewed section is unnecessarily largely opened so that the airbag cannot sufficiently inflate. Additionally, a gas discharge pressure at which gas is discharged from the airbag varies in accordance with the size of the formed gas leak opening, and therefore a uniform gas discharge pressure cannot be obtained throughout many products. This lowers the reliability of the product. In view of this, it has been proposed to fix two reinforcement cloths respectively at the opposite end portions of the low strength sewed part. However, a uniform distance is difficult to be obtained between the two reinforcement cloths throughout many products, and consequently the size of the gas leak opening varies depending upon the distance between the two reinforcement cloths thereby making impossible to obtain the uniform gas discharge pressure throughout many products. Furthermore, since the two reinforcement cloths are used, the number of parts increases while making troublesome an assembly operation of the airbag.